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Smog. View over Mexico City showing a cloud of grey atmospheric pollution (smog). Smog occurs when atmospheric pollution builds up in city air. Modern city smogs are caused by car exhaust fumes, industrial emissions and the domestic burning of fossil fuels. Air pollution can have detrimental effects on the environment. As well as health risks, air pollution causes the deterioration of buildings and tarnishing of metals. One of the major health risks are caused by the excess of toxic gases such as ozone in a polluted atmosphere. Excessive amounts of lower atmospheric ozone can irritate and scar breathing passages and lungs.